Electrical inductive apparatus having sheet and strap wound windings

ABSTRACT

A power distribution transformer having a multiple section highvoltage winding. At least one section is wound from sheet conductor material. Another section is wound from strap conductor material and is disposed concentrically around the sheet wound section. Tap leads are attached to the strap wound section and are connected to tap changing apparatus. The setting of the tap changing apparatus determines the extent to which the strap wound section is connected in series with the sheet wound section, and thus determines the voltage rating of the high-voltage winding.

[ 1 Feb. 12, 1974 United States Patent 1191 Michel ELECTRICAL INDUCTIVEAPPARATUS FOREIGN PATENTS OR APPLICATIONS HAVING snEET AND STRAP WOUNDWINDINGS 1,264,600 3/19 68 Germany 336/150 1,264,836

5/1961 1 France....1.....1..................... 336/150 [75] Inventor:George P. Michel, South Boston,

Primary Examiner-Thomas J. Kozma 73] Assignee: Westinghouse ElectricCorporation,

Pittsburgh, Pa.

Apr. 3, 1973 Attorney, Agent, or FirmJ. R. Hanway [57] ABSTRACT A powerdistribution transformer having a multiple [22] Filed:

pp 347,509 section high-voltage winding. At least one section is woundfrom sheet conductor material. Another secw 1% 3 m h "c r a "e was L m IM lsm UI .F HUM 555 tion and are connected to tap changing apparatus.The setting of the tap changing apparatus determines the extent to whichthe strap wound section is connected References Cited UNITED STATESPATENTS in series with the sheet wound section, and thus determines thevoltage rating of the high-voltage winding.

3,113,281 336/150 3,484.72; 336/150 X 4 Claims, 4 Drawing Figures Weberet a1.

BACKGROUND OF THE INVENTION I. Field of the Invention This inventionrelates, in general, to electrical inductive apparatus and, morespecifically, to transformer winding structures.

2. Description of the Prior Art Power transformers frequently have awinding thereof ,tapped so that the voltage rating can be changedconveniently. Normally, the tap leads are connected directly to thewinding of the transformer in which the voltage rating is to be changed.In power-distribution transformers, the high-voltage winding is oftenthe winding which requires a voltage rating change due to variations infeeder line voltages. Thus, it is necessary to provide tap leadsconnected to the high-voltage winding.

Sheet or foil windings are widely used for the highvoltage windings ofdistribution power transformers due to their excellent mechanicalcharacteristics and for other advantageous reasons. However, connectingtap leads to sheet conductors is relatively complicated and requiresspecial techniques. Therefore, it is desirable, and it is an object ofthis invention, to provide a transformer having a high-voltage windingstructure which is substantially wound from sheet conductors and whichcan be conveniently connected tov tap leads.

Sheet windings contain at least one foil layer spirally wound around thepreceding turn of the foil layer. Since the inner turns of the foillayer are inaccessible when the winding is completely wound, tap leadsmust .be connected to the winding during the construction process. Thistechnique requires considerable time and presents difficulties ininsulating the tap lead as it is brought axially to the outside of thewinding. Therefore, it is also desirable, and it is another objectof-this invention, to provide a transformer which has a primary windingsubstantially wound-from sheet conductor and which is easily tappedafter the sheet conductors have been wound.

7 SUMMARY OF THE INVENTION There is disclosed herein a new and usefultransformer having a novel arrangement for tapping the sheet or foilwinding of the transformer. In one embodiment, the sheet winding iswound into two sections which are substantially concentrically disposedabout a common axis. A tapped winding wound with strap conductors isalso concentrically disposed around the common axis and around theoutside of the sheet windings. Tap leads and end leads are attached tothe tapped winding and are connecte'd to the sheet winding sections bysuitable jumpers or tap changer contacts to electrically place thetapped winding between the sheet winding sections. In anotherembodiment, the sheet winding has only one section and the tappedwinding is electrically connected to an'end of the sheet winding. Inboth embodiments, all of the tap leads are attached to the strapwinding. The strap winding is physically located on the outside of thesheet windings where the taps can be made conveniently. This positioningof the tapped winding also places it outside of the high leakage fluxregion, thus minimizing'the impedancechange as the tap position ischanged.

BRIEF DESCRIPTION OF THE DRAWING Further advantages and uses of thisinvention will become more apparent when considered in view of thefollowing detailed description and drawing, in which:

FIG. 1 is a view of a transformer constructed according to thisinvention with a portion of a winding structure cut-away for clarity;

FIG. 2 is a sectional view, shown schematically, taken generally alongthe line llII of FIG. 1;

FIG. 3 is an electrical schematic diagram of the transformer shown inFIG. 1; and

FIG. 4 is an electrical schematic diagram of a transformer constructedaccording to an embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 10 constructed according tothis invention. The frame structure 12 encloses and supports athree-phase magnetic core 14 having three core legs, such as core leg15. Around the legs of the magnetic core 14 are disposed the windingstructures l6, l8 and 20.

The cut-away portion of FIG. 1 illustrates the details of the windingstructure 20. Winding structures 16 and 18 are constructed similar tothe winding structure 20. A low-voltage winding 22 is constructed of aplurality of turns of a suitably shaped conductor. Either sheet or strapconductor material may be used with appropriate insulating materialdisposed between the turns of the conductor. The conductor is woundaround the leg 15 of the magnetic core 14.

A high-voltage winding section 24 is constructed of a plurality of turnsof a foil or sheet'conductor. A highvoltage winding section 26 issimilarly constructed. The high-voltage winding section 24 is woundaround the low-voltage winding 22 and the high-voltage winding section26 is wound around the high-voltage winding section 24. The high-voltagewinding may comprise only one sheet wound section in particular types oftransformers, such as transformers which will have the high-voltagewindings connected only in a wye arrangement. Leads 28 and 30 areconnected to winding section 24 and leads 32 and 34 are connected towinding section 26. The leads 36 and 38 are connectedto the windingsection 22. j

A tapped high-voltage winding 40 is constructed of a plurality of turnsof a strap conductor wound around the winding section 26. The turns mayspiral in an axial direction with a radial build equal to the thicknessof one strap, or in a radial and axial direction with a radial buildequal to the thickness of several straps. The leads 42 are connected totap and end terminals on the tapped winding 40.

Using a sheet conductor for the major part of the high-voltage windingpermits the advantages for which sheet conductors offer, such asexcellent short circuit strength. Using a strap conductor for the tappedportion of the high-voltage winding permits easy connection of the tapleads to the tapped winding 40.

Foil or sheet conductors are relatively thin compared to strapconductors. In sheet conductors, the thickness of the sheet issubstantially less than the axial height of the sheet. In strapconductors, the conductor dimensions along the axial and radialdirections of the windings are of the same order of magnitude, with suchdimensions usually having a ratio of less than ten.

FIG. 2 is a view, shown schematically, taken generally along the linell-lll of FIG. 1. The leads 44 and 46 are connected to the ends of thetapped winding 40. Leads 48, 50 and 52 are connected to tap terminals onthe winding 40. Since winding 40 is located on the outside of thewinding structure 20, the tapped winding 40 is readily accessible formaking the tap connections.

The end and tap leads 42 are illustrated in FIGS. 1 and 2 as beingbrought to the top of the winding structure for connection to suitablejumpers or to tap changing apparatus. It is within the contemplation ofthis invention that the leads 42 may project from the winding structure20 in other places, such as along the outside of the winding structure20 near the position where the lead is connected to the winding 40. Theleads 28 and 34 of the high-voltage windings 24 and 26 are line leadswhich are normally connected to, or electrically close to, thehigh-voltage line.

FIG. 3 is a partial schematic diagram of the transformer shown in FIGS.1 and 2. As is best shown in FIGS. 1 and 2, the winding 40 is physicallypositioned around the outside of the high-voltage winding in arelatively low leakage flux region. However, electrical considerations,such as surge voltage strength, make it desirable to locate the winding40 electrically near the center of the high-voltage winding as shown inFIG. 3.

FIG. 3 illustrates the electrical jumper connections required to providea voltage rating which is one step below the maximum voltage rating.Jumper connections 56 and 58 normally are provided by a tap changerconnected to the leads. Changing the voltage rating involves changingthe position of one or both of the jumper connections in a manner wellknown in the art.

F 10.4 is a partial schematic diagram of a transformer having a windingarrangement constructed according to another embodiment of thisinvention. When a transformer will be only Wye-connected, it isacceptable practice to place the tapped winding near the common end ofthe high-voltage winding. Such placement does not subject the tappedwinding to surge voltages near the line end of the winding since thecommon end of the winding is not connected to the high-voltage line. InFIG. 4, the high-voltage winding 60 has only one winding section, thusno intermediate leads are required. Winding 40 is physically positionedas shown in FIGS. 1 and 2. However, according to the embodiment shown inFIG. 4, winding 40 is electrically connected to the end of thehigh-voltage winding 60 by a suitable tap changer or by a suitablejumper connection 62. Other taps may be connected by the jumperconnection 62 to provide a different voltage rating.

The embodiments of this invention provide a convenient and functionalmanner for constructing a high strength, high-voltage winding for apower distribution transformer. Although described with reference to aprimary high-voltage winding, the invention applies equally tolow-voltage secondary windings and to secondary windings of step-up"transformers. Since numerous changes may be made in the above-describedapparatus, and since different embodiments of the invention may be madewithout departing from the spirit thereof, it is intended that all ofthe matter contained in the foregoing description, or shown in theaccompanying drawing, shall be interpreted as illustrative rather thanlimiting.

I claim as my invention:

1. Electrical inductive apparatus comprising:

a magnetic core;

a low-voltage winding disposed around a leg of said magnetic core;

a high-voltage winding comprising a conducting sheet wound around saidlow-voltage winding to form a plurality of winding turns;

a tapped high-voltage winding comprising a conducting strap wound aroundsaid high-voltage sheet wound winding to form a plurality of windingturns; and

a plurality of tap leads connected to said tapped highvoltage windingand being suitable for connection to the high-voltage sheet woundwinding;

said low-voltage, high-voltage sheet wound, and

tapped high-voltage windings being disposed substantially concentricallywith each other and around said leg of said magnetic core.

2. The electrical inductive apparatus of claim 1 wherein the highvoltage sheet wound winding is divided into first and second sectionswith the tapped high-voltage winding being connectable electricallybetween said first and second high-voltage sheet wound winding sections.

3. The electrical inductive apparatus of claim. 1 wherein the magneticcore includes first, second and third legs, each of said legs havingdisposed concentrically therearound a low-voltage winding, ahigh-voltage sheet wound winding, and a strap wound tapped highvoltagewinding.

4. A power transformer comprising:

a three-phase magnetic core having first, second and third legs;

first, second and third low-voltage windings wound around said first,second and third legs, respectively;

first, second and third sheet wound high-voltage winding sections woundaround said first, second and third low-voltage windings, respectively;

fourth, fifth and sixth sheet wound high-voltage winding sections woundaround said first, second and third high-voltage winding sections,respectively;

first,- second and third strap wound tapped highvoltage windings woundaround said fourth, fifth and sixth sheet wound high-voltage windingsections, respectively;-

line terminals connected to said first, second, third, fourth, fifth andsixth sheet wound high-voltage winding sections;

end terminals and at least one tap terminal connected to said first,second and third tapped high-voltage windings; and

means for connecting said line, end and tap terminals together to changethe voltage rating of the transformer.

1. Electrical inductive apparatus comprising: a magnetic core; alow-voltage winding disposed around a leg of said magnetic core; ahigh-voltage winding comprising a conducting sheet wound around saidlow-voltage winding to form a plurality of winding turns; a tappedhigh-voltage winding comprising a conducting strap wound around saidhigh-voltage sheet wound winding to form a plurality of winding turns;and a plurality of tap leads connected to said tapped high-voltagewinding and being suitable for connection to the high-voltage sheetwound winding; said low-voltage, high-voltage sheet wound, and tappedhighvoltage windings being disposed substantially concentrically witheach other and around said leg of saiD magnetic core.
 2. The electricalinductive apparatus of claim 1 wherein the high voltage sheet woundwinding is divided into first and second sections with the tappedhigh-voltage winding being connectable electrically between said firstand second high-voltage sheet wound winding sections.
 3. The electricalinductive apparatus of claim 1 wherein the magnetic core includes first,second and third legs, each of said legs having disposed concentricallytherearound a low-voltage winding, a high-voltage sheet wound winding,and a strap wound tapped high-voltage winding.
 4. A power transformercomprising: a three-phase magnetic core having first, second and thirdlegs; first, second and third low-voltage windings wound around saidfirst, second and third legs, respectively; first, second and thirdsheet wound high-voltage winding sections wound around said first,second and third low-voltage windings, respectively; fourth, fifth andsixth sheet wound high-voltage winding sections wound around said first,second and third high-voltage winding sections, respectively; first,second and third strap wound tapped high-voltage windings wound aroundsaid fourth, fifth and sixth sheet wound high-voltage winding sections,respectively; line terminals connected to said first, second, third,fourth, fifth and sixth sheet wound high-voltage winding sections; endterminals and at least one tap terminal connected to said first, secondand third tapped high-voltage windings; and means for connecting saidline, end and tap terminals together to change the voltage rating of thetransformer.